Fill color with opacity.Note: If color is set as a string (e.g. 'red .5') it has a priority over opt_opacity, which
means: color set like this rect.fill('red 0.3', 0.7) will have 0.3 opacity.Note: Works only with anychart.core.cartesian.series.Bubble#displayNegative.

Fill color with opacity.Note: If color is set as a string (e.g. 'red .5') it has a priority over opt_opacity, which
means: color set like this rect.fill('red 0.3', 0.7) will have 0.3 opacity.Note: Works only with anychart.core.cartesian.series.Bubble#displayNegative.